Generally, control and health monitoring in harsh environments require robust electronic component and interconnect system designs. In systems such as gas turbine engines, constraints often apply to the allowable weight, cost and reliability of the interconnect system. These metrics are often traded during the design process to get the best result. As systems become more complex, the interconnect count between system components increases which also increases system complexity. With the increase in interconnects, troubleshooting systems do not always identify the contributing faulty components reliably in the event that system anomalies occur.
Difficulty in troubleshooting systems that have electronic components connected to control system devices such as actuators, valves or sensors arises from multiple potential sources for system faults. For example, a noisy signal in a sensor reading could be caused by a faulty interface circuit in the electronic component, a faulty wire or short in the cable system, or a faulty or intermittent sensor.
The time associated with identifying a faulty component quickly and accurately affects operational reliability, i.e. the ability to dispatch a flight on time. If the delay persists for too long, costly flight delays can occur. If the faulty component is identified improperly and returned to a supplier for testing, no faults will be found and the cost of the return will be wasted.
Another problem is that tracking usage on all control and health monitoring components is difficult. Typically, the electronics that can measure and record component faults are not part of the component that requires tracking. Separating the information from the component presents a logistics puzzle for maintainers that manage the parts and data. If component specific tracking information were available, it would hold significant value for the maintainer. The information could be used to predict impending failures and predict remaining life, even if the component were to be installed on several engines throughout the component's life.
Another issue is that to increase efficiency in gas turbine engines, component variability that contributes to system uncertainties needs to be reduced. One costly way to address uncertainties is to add cost with more expensive parts or tighter tolerances on existing designs. Another way would be to characterize a component during acceptance testing and store the characterization in memory for use by the control system in reading parameters or scheduling actuators. With typical systems, this approach is difficult because most control system components such as fuel controls, actuators and sensors do not typically contain on-board memory.
Additionally, electronic components experience temperatures that may vary over a wide range. For example, at a typical 35,000 feet (10668 meters) altitude, the ambient temperature will likely be approximately −65° F. On a hot day, the ambient temperature plus solar radiative heat may be approximately 190° F. at sea level static conditions. Military components can see even hotter temperatures due to ram air inlet conditions during flight. There are two damaging aspects of the varying thermal environment. The first damaging aspect is the temperature cycles between extreme cold ambient air temperatures and high temperatures caused by ambient conditions coupled with internal heating effects. These thermal cycles stress internal components and solder joints because of differences in their respective thermal expansion coefficients. The cycles happen during every engine flight. The second damaging aspect is that the extreme hot ambient air temperatures over extended periods along with internally generated heat may degrade electronics and eventually cause loss of wire bonding in integrated circuits or cracked solder joints on circuit boards. This can cause integrated circuits to malfunction at extreme high or low temperatures without immediate physical damage observable to the naked eye.